1. Field of the Invention
This invention relates generally to professional cinematography; and more particularly to accessory apparatus for use with existing, standard professional motion-picture cameras, and to methods for cinematographic photography.
2. Prior Art
In still photography, as distinguished from motion-picture work, professionals commonly use view cameras that are equipped with adjustments for disposing and orienting a lens variably or selectably in relation to the film plane. Such adjustability is particularly useful, as is well known, for manipulating focal relations and image shapes.
Still photographers know that rotating the film plane relative to an object--for example, relative to the frontal plane of a building being photographed--alters the shape of the object image at the film. This effect is most commonly recognized in photography of geometrically regular objects such as rectangular tall buildings.
(Throughout this discussion, except where otherwise specified, we are referring to rotation of the film plane about an axis that is in a plane which is preferably parallel or nearly parallel to the film plane--or at least about some axis that is not perpendicular to the film plane. Rotation about an axis perpendicular to the film plane does have some utility as we shall describe shortly, but does not in itself alter either focal relationships or image shapes.)
The shape-alteration effect, however, is also present in photography of nonplanar or irregular articles. Thus eggs can be imaged to appear spherical, and billiard balls egg-shaped.
Perhaps somewhat less generally recognized is the fact that rotating the lens plane relative to an object, or relative to the film plane, alters the focus. More specifically, planes of constant focus in the object space (and the corresponding planes in the image space) rotate with the lens plane.
For example, the photographer Ansel Adams used the focal-alteration effect in a classic picture of Mount Williamson. The image includes a mountain range a mile or two away, and in front of it a boulder-strewn plain--the nearest rocks just a few feet away. Both the mountain and the nearest rocks are in sharp focus, a result apparently obtained in part by tilting the lens down to change the plane of sharp focus from vertical to more nearly parallel with the field of boulders.
Creative use of both the shape and focal alterations often produces in the film plane an image of the desired subject that is off center relative to--or even entirely outside of--the photographable frame. Compensation for this undesired result requires transverse motion of the film frame relative to the lens or, to put it more generally, transverse relative motion between the film frame and lens. (Because lenses are most often smaller than cameras, such relative motion is usually described as shifting the lens relative to the camera.)
Such transverse motion in effect displaces the film frame within, but parallel to, the focal plane so as to select for recording within the limited film frame some relatively small part of the focused image. That part need not be near the lens axis or centerline.
In professional view cameras, rotational adjustments of the lens relative to the film plane are provided in two components: rotation about a vertical axis, which is usually denominated "swing"; and rotation about a horizontal axis, usually called "tilt". Similarly, translational adjustments are provided in two components: "shift" or horizontal translation, and "rise-and-fall" or vertical translation.
All these adjustments are usually provided by supporting a lens-board mount as the final element in a sequence of intermediary mechanical elements between the camera and the lens board. Each intermediary element is supported from an earlier element in such a way as to supply one of the translational or rotational movements desired.
View cameras generally have a single, unitary rail for mutual support and longitudinal adjustment (i.e., focus) of the film back and lens board. In some view cameras the first stage or element of the lens-board carriage can be simply slid along the rail and manually clamped at a desired position, and fine adjustment (fine focus) can then be attained by longitudinal rack-and-pinion adjustment of the next element of the lens-board carriage relative to that first sliding element; but in other cameras the first stage itself has a rotatable pinion that engages a long, toothed rack extended along the rail. In all these situations, as will be understood for purposes of this document, each later stage is to be considered as sliding (or moving) relative to its immediately earlier stage--subject to gear means, if present, interconnecting the elements to provide relatively fine manual control of the motion.
In some press-style cameras a pair of outboard rails is substituted for the single, unitary rail. These cameras, however, generally have a much more limited selection and range of different lens/film movements.
The sequence of intermediary mechanical elements continues from the first stage, or first two stages, that supply focal adjustment through other elements supplying swing, tilt, shift and rise-and-fall, to the lens-board mount. A bellows between the lens-board mount and a port on the camera back then seals the optical path against ambient light, so that only image light from the lens can reach the film. This system is desirable in that the bellows accommodates the many possible combinations of swing, tilt, shift and rise-and-fall between the lens and film while maintaining a good light seal.
In recent years, however, a different system has been introduced in accessories for still cameras of the single-lens reflex (SLR) type. In these accessories there is no bellows, and instead a series of intermediary elements is supported from the lens-mounting port of the SLR camera, where a lens is usually placed.
A lens is then mounted to the last of the intermediary elements in the sequence. Light from the lens passes through all or most of the intermediary mechanical elements, and through the lens-mounting port to the film. Substantially all of the movements between successive intermediary elements in such systems, accordingly, must be individually light-sealed.
In some SLR systems the objectionable requirement of individual light seals between all the intermediary mechanical elements or stages is mitigated simply by reducing the number of stages. This can be done simply by foregoing, for example, horizontal movements (swing and shift); and these movements are much less commonly desired than the vertical adjustments (tilt and rise-and-fall). Furthermore, setting aside the limitations of the high-aspect-ratio image format in SLRs, the vertical movements can be substituted for the horizontal ones simply by rotating the camera about the lens axis.
Another approach used in SLR systems, however, is to provide another sort of movement between stages--namely, rotation of the accessory, or some of its stages, about the lens axis. This particular motion is relatively very easy to light-seal, and so adds relatively little complexity or difficulty to the mechanism, but can be used to very effectively convert the vertical movements into horizontal movements.
This approach also has another beneficial result that goes beyond merely reducing the number of difficult optical seals: with this system, focal or geometrical alterations can be effectuated with respect to axes that are neither vertical nor horizontal--and therefore without the necessity for combining separate vertical and horizontal effects to obtain the desired results. This advantage, however, comes into play only in quite unusual situations.
As far as we know, no one has ever provided an accessory for standard motion-picture cameras to supply generally adjustable rotational or translational relative motion of the lens and film.
Perhaps some such accessories have been used in special-effects work with models, such as shots intended to simulate the appearance of enormous spacecraft passing by--in which lens swings may have been coordinated with changes in model position and camera angle to generate exaggerated vanishing-point effects. These, however, are in essence still-camera applications.
We are aware of isolated instances in which individual cinematographers--confronted with a desire to correct (or create) a geometrical or focal distortion, or to use some portion of an image that would normally be outside the film frame--have custom-mounted a lens in an odd position or orientation. Each such customized arrangement has been for purposes of a particular shot, and generally has been set up by using very temporary special mounting provisions--such as supporting part of the lens board in putty, and very carefully moving the lens into a desired position to be maintained by the putty.
As will be evident, such arrangements require special light-sealing provision or other undue effort. They are not amenable to dynamic shots in which the motion-picture camera is mounted on a moving vehicle, pendulum, sling or other carriage--and so cannot be used as a matter of routine.
We are not aware of anyone else having previously considered the possibility of making an attachment for motion-picture cameras to facilitate such routine operation. If such thought has been devoted to this problem, very likely it has been abandoned upon consideration of the difficulties of accommodating the specific geometries of modern cameras that are popular with cinematographic professionals.
As we are not aware of any prior thought having been devoted to this problem, it would be inappropriate to further speculate on specific geometry difficulties under the heading of "prior art." Because our own work that led to the present invention has included very extensive analysis of these problems, we shall discuss them further in the next section--which is devoted to our invention.
Accordingly a problem has existed heretofore in the cinema field--namely, that professional motion-picture-camera operators have not been able to make routine advantage of the composition, image-correction or -distortion, or focal alterations available through swing, shift, tilt or rise-and-fall of a lens relative to a motion-picture camera. Such advantage would include straightforward solutions to a great variety of problems routinely faced in cinematography.
As a simple example, it is common in making motion pictures to photograph two or more people who are at greatly different distances from the camera. To obtain the needed depth of focus without resorting to focal alteration as Adams did in his photograph of Mount Williamson, it is common to lengthen the depth of focus by stopping down the lens to an extreme degree.
This in turn, however, requires a correspondingly extreme overillumination of the scene, resulting in actors' discomfort and relatively unnatural expressions, as well as fatigue. In motion-picture work generally, time exposures are not an option to compensate for the use of very small apertures.
Other possibilities, such as using shorter-focal-length lenses (which exaggerate the size of nearer objects) or faster film (that generally introduces differences of color balance and grain size), each have their own respective drawbacks. Fundamentally, they restrict esthetic control by the director and camera operator.
Other aspects of the existing problem in cinematography include exaggerated vanishing-point effects when photographing tall buildings or horizontally long objects such as railroad trains. These too can be objectionable, and virtually impossible to avoid--especially when panning upward or sideward, respectively.
Still other aspects of the problem arise in use of such favorite dramatic effects as photographing a scene in a mirror. To obtain a very close simulation of the geometric relationships seen by a person who is looking directly into a mirror, it is particularly desirable to be able to point the camera directly toward the mirror, along a perpendicular to the mirror surface.
As this condition is approached, however, of course the cinematographer finds an image of the camera--or of the camera operator--intruding into the scene. To avoid that unacceptable result, the camera must be pointed at a different angle and the feeling of intimacy and realism in the scene thus sacrificed. No such compromise is required when the lens can be shifted laterally relative to the film frame.
From all the foregoing it can be appreciated that the prior art has not solved this problem of providing a generally usable swing/shift/tilt/rise-and-fall accessory for motion-picture use.
In a known area of cinematography not heretofore associated with this problem, photographers have used a hardware accessory called a "balance plate" or "base" for mounting optical accessories such as matte boxes, or to help support very long, heavy lenses. The balance plate is relatively shallow and is mounted below the motion-picture camera--usually between tripod and camera.
It carries a pair of forward-extending cylindrical bars historically known as "iris rods". Usually a bridge structure, mounted to slide along and clamp to the iris rods, supports the optical accessory or long lens.